Vulcanization accelerator



Patented Aug; 7, 1945 v i v i 2,381,384- 1 TMULCANIZATION ACCELERATOR:"Eawala L. can, .Akron, Ohio, assignor to The vFirestone Tire & RubberCompany, Akron, 1

Ohio',"a corporation of Ohio zNo Drawing.

" lI hieairtventionerelates tome vulcanization of JIt'jiS a primary iobject gtheipresent'invention to provide ainewlclass-zof accelerators-forthe vulcanization of ruaitural .or .synthetic rubber.

Another ;object isrto provide a new group of delayed actionrubbervulcanizationaccelerators. .,.Ainother objectis lto providea'irapidmethodof 1 vulcanizing lm bberiatcustomary vulcanizing temperatures. Ifv a J A :further :object' is-w'tolprovide vulcanized rubber of improvedquality,- possessing the characteristics of highmodulus and tensile, lowhystere Sis and a high inherent resistance to deterioration by flexingor aging. 'r f I 1 The above IaDdEfHItiheP.1111160173 will be unani-Hfest. in. the idescripti'on' of; the invention which follows. .1 I

It has. been found :thatlmembers of a new -;c'lass iothhemical compoundsare very effective in accelerating. the {vulcanization of natural orgsyntheticgrubher. The hewkcompounds, may 'be conveniently iprep ared byoxidizing a :mixture of -l-aniaromatic Z-mercaptothiazole and anhydroxyalkyl primai'yiagnine. i The;preparative..oxidation reaction maybe carriedout by tlieatingamixture. :of jthe, :mercaptothiazole :andKQII'CXCGSS .of the amine-man -,alka1ine aqueous "medium with one IDffl-thggfOHQWiTl oxidizi'ngagentsz :chlorine, bromine, iodine..ypQchlorous zacid,jhypobromous acid, shypoiodousracid, -and; al-l a1imetal and alkalinleparth metalsalts of said acids. The oxidationreaction isbelieved to compr se the. direct action of ahypohalousacid,.-oran alkali metal or an alkaline eart h metalsaltthereof, on a mixture of the merc'aptothia'zole and one equivalentof the amine. The desired substances produced hy this oxidation reactionare organic compounds containing nitrogen sulfur. and oxygen.

new :class o accelerators is believed to possess the following type iormulaz AK c-'-s- (|3R Application September 20,1941, Serial No. 411,719

phenylbenzo, naphtho; and homologs or the various' ring substitutionproducts of these radicals;

"asty'p'icalring s ub'stituents there maybe :men-

tioned' nitro, halogen, hydroxy andalkoxy groups. Examples of alkylradicals include niethyL-ethyl, propyl, butyl, amyl, hexyl, heptyl,octyl and similar radicals. Examples of hydroxyalkyl radicals includehydroxymeth yl, alpha-hydroxyethyl, betahydroxyethyl and similarradicals.

The following specific example is given in further illustration of theinvention.

" Example p A solution was preparedLcontaining 10 grams ofmercaptobenzothiazole, 4.8 grams of sodium hydroxide. and 7 gramsofethanolamine in a Volume of 350 cubic centimeters. Into this solution,at room temperature, there was slowly dropped, with stirringfan iodinesolution containinglS grams of iodine-and 15 grams of potassium iodideina volume 0f"150 cubic centimeters." Awhite solid precipitated during theadditi'onbf the iodine solution. After the completion of the additionofthe iodine solution the solidproduct was separateddand recrystallizedfrom a mixture of ether and petroleum ether. The -white, recrystallizedproduct melted at 98- 99 C. The product, so produced, isbelieved to beN-(beta-hydroxyethyl)'-2-benzothiazy1 sulfen'amide of. the -followingformfila:

with the standard accelerator, mercaptobenzo- I hen]; OH H 'I-heabove-reaction product was tested as a rubber vulcanization acceleratorby comparing it thiazole,-

the following'rubber formula:

The two rubber compositions, so formulated, were vulcanized by beingheated at 280 F. for 20, 30 and minutes, and the following physical datawere otbained on the vulcanized compositions:

The above results clearly show that the sulfenamide derivative is a veryeffective rubber accelerator, which imparts consistently higher modulusand tensile characteristics to a rubber composition than does thestandard accelerator, mercaptobenzoth'iazole. Similar results areobtained by the use of other sulfenamide derivatives of the same class,such as N-(alpha,alpha-dimethylbeta-hydroxyethyl)-2-benzothiazylsulfenamide of the formula 'N H CH3 CS1 I-( IJCHQOH \S CH:

and N- [alpha-methyl-alpha- (hydroxymethyl)beta-hydroxyethyl]-2-benzoth'iazyl sulfenamide of the formula These twoderivatives may be prepared by applying the general oxidation reactionmentioned above, respectively, to a mixture of mercaptobenzo'thiazolewith 2-amino-2-methyl-l-propanol and to a mixture ofmercap'tobenzothiazole with 2- amino-Z-methyl-1,3-propandiol.

The preferred. class of sulfenamide derivatives may be prepared by othermethods than th'ose mentioned hereinabove, as will be apparent to oneskilled in the art. For example, a mixture of an aromaticZ-mercaptothiazole and an hydroxyalkyl primary amin' may be oxidized byhydrogen peroxide or other conventional oxidizing agent. The inventionis not limited to derivatives prepared in accordance with any particularmethod, but includes the preferred class of accelerators, howeverAlthough the new accelerators cause rapid vulcanization of rubbercompositions at usual vulcanizing temperatures, they are of the delayedaction type and do not cause set-up or pro-vulcanization of the rubberunder ordinary processing conditions and temperatures. Moreover, the newclass of accelerators may be used in combination with otheraccelerators, such as a guanidine (e. g., .diphenylguanidine) or amercaptothiazole derivative (e. g., mercaptobenzothiazole ordibenzothiazyl disulfide) in order to produce rubber compositions havingspecial vulcanization characteristics, such as the ability to vulcanizecompletely at abnormally low temperatures.

Although sulfur has been given as the only example of a vulcanizingagent, other known vulcanizing agents may be used in the present methodof vulcanizing rubber.

What is claimed is:

1. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of N- (beta-hydroxyethyl) -2-benzothiazylsulfenamide.

2. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of N-(alpha,alphadimethyl-beta-hydroxyethyl)-2'-benzothiazyl sulfenamide.

3. The method of vulcanizing rubber which comprises heating rubber andsulfur in the presence of N [alpha-methyl alpha (hydroxymethyl)beta-hydroxyethyll -2-benzothiazy1 sulfenamide.

4. The method of vulcanizing rubber which comprises heating rubber and avulcanizing agent in the presence or a compound having the formulawherein Ar is an orthoarylene radical, R and R are selected from thegroup consisting of hydrogen, alkyl radicals and hydroxyalkyl radicals,and R is an hydroxyalkyl radical.

5. A vulcanized rubber product prepared by heating rubber and sulfur inthe presence of N- (beta-hydroxyethyl) -2-benzothiazyl sulfenamide.

6. A vulcanized rubber product prepared by heating rubber and sulfur inthe presence of N- (alpha,alpha-dimethyl-beta hydroxyethyl) 2-benzothiawl sulfenamide.

"7. A vulcanized rubber product prepared by heating rubber and sulfur inthe presence of N- [alpha-methyl-alpha- (hydroxymethyl) -beta-hy-

